关键词: 锥度球头刀, 钛合金TC4, 四轴铣削, 残余应力, 逆向辨识, 离散度

Abstract: The internal and external profile finishing of the metal reinforcing edges of the leading edge of large composite fan blades for commercial aero-engines was accomplished by four-axis milling with a customized taper ball-end cutter, and the machining residual stresses introduced at this stage often caused excessive bending and torsional deformations leading to dimensional overshoots of the parts. For the four-axis milling of titanium alloy TC4 with taper ball-end cutter, an inverse identification method of milling residual stress gradient distribution was proposed based on the deformation tests of thin plate machining herein. The hyperbolic tangent models were used to parametrically characterize the milling residual stress gradient distribution, and the solution of the residual stress gradient distribution was converted into the inverse solution of two pending coefficients k and ω. The model coefficient k was determined by testing the residual stress on the machined surfaces of the titanium alloy specimen blocks, and the model coefficient ω was inversely solved by testing the bending deformation deflection of milled titanium alloy thin plates, then the residual stress gradient distribution curve was determined. Four groups of titanium alloy TC4 test block milling validation experiments were carried out, and the test results show that the average prediction accuracy of the milling residual stress gradient distribution is as high as 99.35%. Compared with the traditional X-ray test method, the proposed method avoids the use of electrolytic corrosion stripping to test the subsurface residual stresses, and also takes into full consideration the non-uniformity of the distribution of milling residual stresses on the machined surfaces, namely the problem of the dispersion of milling residual stresses.

Key words: tapered ball-end cutter, titanium alloy TC4, four-axis milling, residual stress, reverse identification, dispersion